Method of preventing formation of harmful combustion gases in combustion furnace

ABSTRACT

There is provided a method for considerably reducing the harmful constituents of exhaust gases ejected into the atmosphere from the combustion chamber of a combustion furnace such as a melting furnace, direct heating furnace, indirect heating furnace or reaction furnace when a mixture or fuel is burned therein. A novel feature of this method is that a mixture of oxygen and either an inert gas or the exhaust gas from the combustion chamber is substituted for practically the whole quantity of air fed to the combustion chamber to burn the fuel therein.

"United States Patent 1191 Konda [4 1 Sept. 16, 1975 METHOD OF PREVENTING FORMATION OF HARIVIFUL CONIBUSTION GASES IN COMBUSTION FURNACE [75] Inventor:

[73] Assignee: Denyo Kagaku Kogyo Kabushiki Kaisha, Tokyo, Japan 22 Filed: Dec. 17,1973

21 Appl. No.: 425,621

Kichiro Konda, Tokyo, Japan 3,146,821 9/1964 Wuetig 431/9 X 3,730,668 5/1973 lida et a1... 431/10 3,746,498

7/1973 Stengel 431/4 Primary ExaminerEdward G. Favors Attorney, Agent, or FirmMichae1 S. Striker 57 ABSTRACT There is provided a method for considerably reducing the harmful constituents of exhaust gases ejected into the atmosphere from the combustion chamber of a combustion furnace such asa melting furnace, direct heating furnace, indirect heating fumace or reaction furnace when a mixture or fuel is burned therein. A novel feature of this method is that a mixture of oxygen and either an inert gas or the exhaust gas from the combustion chamber is substituted for practically the whole quantity of air fed to the combustion chamber [56] References Cited to burn the fuel therein.

UNITED STATES PATENTS 2,417,835 3/1947 Moore 431/ 158 5 Claims, 1 Drawing Figure l 211 204 206 222 ,1 i i METHOD OF PREVENTING FORMATION OF HARMFUL COMBUSTION GASES IN COlVIBUSTION FURNACE BACKGROUND OF THE INVENTION The present invention relates to a method for considerably reducing the amounts of the noxious combustion constituents of the exhaust gases ejected into the atmosphere from combustion chambers of various kinds.

Many different kinds of combustion fumaces in which coal, coke, petroleum, gas, etc. is burned, are' widely used in the smelting and processing of iron and steel and various other metals, the manufacturing of gases, cokes, cement, glass, etc. and many other industrial fields. The exhaust gases emitted to the atmosphere from these combustion furnaces include harmful substances such as carbon monoxide (CO), hydrocarbons (I-ICs) and oxides of nitrogen (NOx), and increasingly strict control of the emission of these harmful gases has been demanded as the problem of socalled environmental sanitation. However, no industrially suitable effective measure for controlling these harmful gases, particularly nitrogen oxides has been developed and in the present circumstances, therefore, the operation of such combustion furnaces must be cut in case of emergency.

In view of the fact that said harmful constituents of exhaust gases are produced from the incomplete combustion of fuel, the inventor, after an experiment wherein an additional supply of oxygen was mixed into the air to be supplied into the combustion chamber of combustion furnace, found that, under the condition, nitrogen oxides tend to increase in quantity while carbon monoxide, hydrocarbons and soots decrease. The inventor further ascertained that the above phenomenon was attributable to the over-supplying of oxygen, which realized complete combustion of fuel on the one hand, and to the complete combustion itself in air containing a considerable quantity of nitrogen at high temperature, caused by complete combustion of fuel on the other. Thus, he hit upon the idea of carrying out the combustion of fuel without supplying the air, the best method to prevent the production of nitrogen oxides during the combustion of fuel in the combustion furnace. However, it has, according to the experiment made by the inventor, become known that the combustion of fuel does not always attain a state of stability, and tends to cause a high temperature in the combustion furnace when an additional supply of oxygen is mixed in greater quantities relative to those of the fuel supplied.

SUMMARY OF THE INVENTION With a view to overcoming the foregoing difficulty, it is an object of the present invention to provide a method of preventing the formation of harmful combustion gases which can be applied easily and conveniently to the combustion chambers of various kinds of combustion fumaces and which is capable of not only effectively reducing the emission of harmful combustion products, e.g., carbon monoxide, hydrocarbons and nitrogen oxides, but also contributing to the improvement of combustion efficiency and the reduction of fuel consumption.

It is another object of the present invention to provide a method of preventing the formation of harmful combustion gases wherein a mixture of oxygen and either an inert gas, except nitrogen, or the exhaust gas emitted from a combustion chamber is supplied into the combustion chamber in place of practically the whole quantity of the air to be supplied to the combustion chamber, thereby preventing the production of nitrogen oxides (NOx) during the combustion of the fuel in the combustion chamber.

DESCRIPTION OF THE DRAWING FIG. 1 is a schematic diagram showing one form of the apparatus for performing the method of this invention, wherein a mixture of oxygen and either an inert gas or the exhaust from a combustion chamber is supplied into the combustion chamber.

DETAILED DESCRIPTION OF THE INVENTION Referring now to FIG. 1 illustrating one form of an apparatus for performing the method of this invention, a combustion furnace 201 is of the ordinary type and it has a substantially closed combustion chamber 202. In this type of direct heating furnace, a heating unit 203 is placed within the combustion chamber 202. The combustion furnace 201 is provided with a fuel supply port 204, a mixture supply port 205 and an exhaust port 206 which are arranged at suitable positions. A fuel such as petroleum, gas or pulverized coal is 'supplied from a fuel source (not shown) to the fuelsupply port 204 by way of a pipe line 221 provided with a valve 21 1. If coal or coke in pulverized or massive form is employed as fuel, a suitable fuel supply system may be provided.

The mixture supply port 205 is connected to an oxygen source 230 through a pipe line 222 having a valve 212 and it is also connected to an inert gas source 231 through a pipe line 223 having a valve 213. The oxygen source 230 includes an oxygen storage means such as a high pressure oxygen bomb or low pressure oxygen container, or it may comprise an oxygen generator having a storage means and pressure means so that a predetermined amount of oxygen is supplied. The inert gas source 231 includes an inert gas storage means such as a high pressure inert gas bomb or low pressure inert gas container or it may comprise an inert gas producer hav ing a storage means and pressure means so that a predetermined amount of inert gas is supplied. While the inert gas should preferably be carbon dioxide gas, any other rare gas such as xenon, argon, neon or helium or a mixture of more than two of these inert gases may also be used. However, such an inert gas as nitrogen gas that will produce harmful gases when subjected to elevated temperatures along with the fuel and oxygen should not be used. Further, while the oxygen and inert gas may be stored in liquid form, they should be vaporized and, if necessary, they should be preheated before they are supplied into the combustion chamber.

The exhaust port 206 is connected to the mixture supply port 205 through a pipe line 224 provided with a valve 214 and it also communicates with the atmosphere through a pipe line 225 provided with a valve 215. On the other hand, the mixture supply port 205 communicates with the atmosphere through a pipe line 226 provided with a valve 216.

While not shown in FIG. 1, there are many other component parts that may be provided as the case may be. They include a flow regulating valve provided in the pipe line 221 to control the quantity of fuel supply, a flow regulating valve provided in the pipe line 222 to control the quantity of oxygen supply in accordance with the quantity of fuel supplied, a flow regulating valve provided in the pipe line 223 to control the quantity of inert gas supply in accordance with the quantity of oxygen supplied, a temperature detecting means and a pressure detecting means provided in each of the pipe lines 222, 223 and 221 for detecting the temperature and pressure of the gas flowing therethrough, a control circuit comprising operators, etc., for supplying control signals to each of the flow regulating valves in accordance withthe detected temperature and pressure, an air blower. provided in each of the pipe lines 224 and 226, a mixing chamber provided at the entry side of the mixture supply port 205 tornix the oxygen, inert gas or exhaust gas, and a heat exchanger provided at the outlet'side of the exhaust port to preheat the oxygen, inert gas or the mixture, thereof and the fuel. The combustion furnace 201 may consist of an indirect heating furnace or any oneof many different types of combustion furnaces. If it comprises an open type furnace, it should preferablybe arranged so that the exhaust is supplied ;it}the.valves 212, 213 and 214 are closed and the valves 21,1 and 216 are opened to supply the air and fuel intothe combustion chamber 202, the usual combustion with the air takes place in the same manner as in the conventional apparatus and thus the exhaust gases containing harmful substances are emitted through the pipe line 225. Consequently, the valve 216 and the pipe line 226 are provided for emergency purposes as the occasion demands. Thus, if they are provided, the valve 216 is normally kept in the closed condition and it is opened temporarily only when it is impossible to supply a sufficient quantity of the oxygen from the oxygen source 230, but the continued combustion is required.

When there is residual air in the combustion furnace 201 during the starting period, the valves 211 and 214 are-closed and then the valves 212, 213 and 215 are opened to substitute the mixture for the air in the combustion furnace 201. Thereafter, the valves 211 and 212 are opened to supply the fuel and the inert gas con- ,taining the proper quantity of the oxygen corresponding to the fuel quantity supplied, i.e., the mixture into the combustion chamber 202. When combustion takes place in this way, the fuel is almost completely burned in the combustion chamber 202, and since no nitrogen .is supplied, the amounts of harmful substances contained in the exhaust gases emitted through the pipe line 225 are reduced considerably as compared with the conventional apparatus where the air is used. In this case, if the valve 214 is opened and the valve 213 is closed while suitably decreasing the opening of the valve 215 to recirculate the exhaust to be supplied into the combustion chamber 202 in place of the inert gas, substantially complete combustion takes place as previously described and thus the exhaust gases emitted through the pipe line 225 contain very small quantities of the harmful substances. In other words, if the air in the combustion chamber 202 is replaced with the inert gas or the inert gas containing the proper quantity of the 'oxygen during the starting period, thereafter the whole or part of the inert gas may be replaced with the recirculating exhaust with the result that the heat loss decreases as the proportion of the exhaust gas increases and moreover a saving in the inert gas consumption may be ensured. Further, evenwhen the proportion of the oxygen in the mixture is slightly lower than that of the oxygen inthe air, a sufficiently; good combustion can generally, take place. e I i Table 1 shows by way of example the results of the tests conducted-using an ordinary metal heating furnace of about.9,000l volume as combustion, furnace.

. The fuel used was a commercially available petroleum and the percentage (weight percentage) of the O in the mixture was gradually changed from 5 to 30 percent with the remainder being CO or the exhaust. After the combustion conditions and the furnace temperatures became practically stable, the relative percentages of the contents of the harmful constituents, i.e., nitrogen oxides (NOx), carbon monoxide .(CO and hydrocarbons (HCs) in the exhaust gases and the furnace temperatures were measured. As shown in case B in the table, when the air was used, the percentages of the NOx, CO and HC. contents were 25,000, 8,500 and 1,500 ppm, respectively. On the contrary, as shown in Case A, when the mixtures according to the present invention were used, the percentages of the contents of the harmful constituents decreased with increase in the percentage of the 0 content up to about 20 percent after which the percentage of the harmful emissions remained unchanged; As compared with the results obtained with the use of the air, the percentages of, the NOx, CO and HC contents were reduced to about l/250, 1/ 10.6 and U15, respectively. On the other hand, when the percentage of the 0 content was higher than 15 percent, the furnace temperature showed about 1100C which was approximately the same as that obtained with the use of the air. In other words, if the percentage of the oxygen, content is maintained at about 15 percent, the required furnace .temperature may be ensured and in this case the percentages of the NOx, CO and HC contents may be considerably reduced to about l/2 50, 1/6.4 and 1/5, respectively, as compared to those obtained when the air was used.

Table 2 shows by way-of example the results of the similar tests conducted using a boiler having a fire bed area of about 10 m as a combustion furnace and a commercially available petroleum as fuel. It was confirmed that the results of the tests showed practically the same tendency withthe results of the tests of Table 1, although some slight differences were noted in the relative percentages of the harmful emissions due to the relatively lower furnace temperatures. It is selfevident that the particularly noticeable reductions in the percentages of the NOx contents are attributable to the elimination of the use'of air in both cases.

TABLE l-Continued Mixture Relative percentages of Furnace by weight) the harmful constituents temper:

in exhaust gases (ppm) ature (C) Case 0, CO, or N0,

exhaust 8 Air 25000 3500 lSOO l I00 TABLE 2 Mixture Relative percentages of Fire bed by weight the harmful constituents temperain exhaust gases (ppm) ture (C) Case 0, CO, or NO, CO HC exhaust 5 95 (Unstable combustion) 8 92 200 I I000 150 600 l0 90 150 5500 100 620 I3 87 100 2700 70 650 A 85 50 l lSO 50 680 18 82 50 500 50 700 20 80 50 350 30 700 75 50 350 700 30 70 50 350 30 700 B Air 22000 13600 300 700 It will thus be seen from the foregoing description that in accordance with the present invention, as described hereinbefore, practically the whole quantity of the air to be supplied into the combustion chamber of a combustion fumace or the like, is replaced with the supply of a mixture of oxygen and either an inert gas other than nitrogen or the exhaust from the combustion chamber, and there is thus provided a method for preventing the formation of harmful combustion products in a combustion furnace which is capable of considerably reducing the amounts of harmful constituents, e.g., nitrogen oxides, carbon oxides and hydrocarbons contained in the exhaust gases emitted to the atmosphere from the combustion chamber of the combustion furnace. e

The present invention is not to be limited to the specific embodiments described hereinafter, but is applicable within the principles enunciated herein to various kinds of combustion furnaces.

What is claimed is:

1. In a process wherein a fuel is combusted, the improvement which comprises combusting said fuel in an atmosphere which is substantially free of chemically uncombined nitrogen so as to reduce the quantities of harmful combustion constituents in the exhaust gases generated during combustion of said fuel, said atmosphere comprising a mixture of oxygen and at least a portion of said exhaust gases.

2. In a process wherein a fuel is combusted, the improvement which comprises combusting said fuel in an atmosphere which is substantially free of chemically uncombined nitrogen so as to reduce the quantities of harmful combustion constituents in the exhaust gases generated during combustion of said fuel, said atmosphere comprising a mixture of oxygen and an inert gas.

3. A process as defined in claim 2, wherein said inert gas comprises at least one of the gases selected from the group consisting of helium, argon, neon, xenon and carbon dioxide.

4. A process as defined in claim 2, wherein said atmosphere comprises a minimum of approximately 15 percent by weight of oxygen.

5. In a process wherein a fuel is combusted, the im provement which comprises combusting said fuel in an atmosphere which is substantially free of chemically uncombined nitrogen so as to reduce the quantities of harmful combustion constituents in the exhaust gases generated during combustion of said fuel, said atmosphere comprising a maximum of approximately 20 percent by weight of oxygen. 

1. IN A PROCESS WHEREIN A FUEL IS COMBUSTED, THE IMPROVEMENT WHICH COMPRISES COMBUSTING SAID FUEL IN AN ATMOSPHERE WHICH IS SUBSTANTIALLY FREE OF CHEMICALLY UNCOMBINED NITROGEN SO AS TO REDUCE THE QUANTITIES OF HARMFUL COMBUSTION CONSTITUENTS IN THE EXHAUST GASES GENERATED DURING COMBUSTION OF SAID FUEL, SAID ATMOSPHERE COMPRISING A MIXTURE OF OXYGEN AND AT LEAST A PORTION OF SAID EXHAUST GASES.
 2. In a process wherein a fuel is combusted, the improvement which comprises combusting said fuel in an atmosphere which is substantially free of chemically uncombined nitrogen so as to reduce the quantities of harmful combustion constituents in the exhaust gases generated during combustion of said fuel, said atmosphere comprising a mixture of oxygen and an inert gas.
 3. A process as defined in claim 2, wherein said inert gas comprises at least one of the gases selected from the group consisting of helium, argon, neon, xenon and carbon dioxide.
 4. A process as defined in claim 2, wherein said atmosphere comprises a minimum of approximately 15 percent by weight of oxygen.
 5. In a process wherein a fuel is combusted, the improvement which comprises combusting said fuel in an atmosphere which is substantially free of chemically uncombined nitrogen so as to reduce the quantities of harmful combustion constituents in the exhaust gases generated during combustion of said fuel, said atmosphere comprising a maximum of approximately 20 percent by weight of oxygen. 